You want my honest opinion? I think you should've noticed the shot elastic. I only notice it now in the pic b/c you mentioned it, as a buyer I probably wouldn't have. As a seller, I'd offer a total refund, b/c she has to pay to ship them back to you, yk? I'd just eat the couple of dollars and re-sell for their real condition. because shot elastic should usually be FFS.
Also, I think it's very immature to ignore someone after a transaction like that. You should reply to each pm and try to handle it maturely. Even if she can fix them, I think it's ok for her to change her mind. I know if I received those diapers I would be extremely upset.

Well said.

As the buyer I would never have noticed the lack of elasticity unless it was pointed out in the description. In those situations I think it should be menioned. I mean, if there wa a signficant stain you wouldn't not mention it, and then call it their fault when it's brought up after they received them. I just think it's rather rude to not follow up with a transaction by at least communicating with her. As far as her "fixing" them, I don't think that is her responsibility. She didn't by diapers that needed fixing.